1. Field of the Invention
The invention relates to a DC electromagnet, in particular for an electric switching apparatus, comprising a magnetizable yoke in the form of a pot having:
a central core, PA1 a coil disposed in this pot concentrically to the core, and PA1 a mobile armature subjected to the action of a return spring and whose peripheral pole surfaces, having a form which increases their values, cooperate with surfaces having the same shape carried by an annular skirt of the pot, through a working air gap which is placed magnetically in series with an air gap closing the flux.
2. Description of the Prior Art
Such electromagnets which are for example known from French patent n. 1 051 651, have advantages and disadvantages with which the user must be satisfied when he contemplates applying them to particular fields; among the advantages must be mentioned the fact that the surfaces of the two air gaps participate at the same time in generating the initial return force; however, because of the ratio of the surfaces of these two air gaps, on the one hand, and because of the presence of two air gaps in series in the magnetic circuit, on the other, it has been discovered that the initial flux is not very high and that, although the induction is relatively high in the core, its value on the peripheral air gap remains low, so that for given ampere turns the initial pull cannot reach interesting values, or, in order to reach these values, it becomes necessary to increase the volume of the coil.